dt-bindings: firmware: arm,scmi: Add missing vendor string

Recently introduced max-rx-timeout-ms optionao property is missing a
vendor prefix.

Add the vendor prefix so that it aligns with the new properties that
are about to get added soon.

Fixes: 3a5e6ab ("dt-bindings: firmware: arm,scmi: Introduce property max-rx-timeout-ms")
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Message-Id: <20241028120151.1301177-7-cristian.marussi@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>

Author: cris-ma

Documentation/devicetree/bindings/firmware/arm,scmi.yaml

@@ -124,7 +124,7 @@ properties:
       atomic mode of operation, even if requested.
     default: 0
 
-  max-rx-timeout-ms:
+  arm,max-rx-timeout-ms:
     description:
       An optional time value, expressed in milliseconds, representing the
       transport maximum timeout value for the receive channel. The value should